Integrated switch-mode power supply and linear regulator

ABSTRACT

A power supply includes a switching voltage regulator, and a linear voltage regulator coupled electrically in series with the switching voltage regulator. The switching voltage regulator includes a first input for receiving a DC input signal, a semiconductor switching stage coupled to the first input and configured to provide a first DC voltage signal from the received DC input signal. The magnitude of the first DC voltage signal is less than the received DC input signal. The linear voltage regulator includes a semiconductor current pass stage coupled to the output of the semiconductor switching stage and configured to provide a constant second DC output voltage signal from the first DC voltage signal. The voltage regulators are implemented together within a common integrated circuit housing.

FIELD OF THE INVENTION

This invention relates to a low noise, high efficiency power supply. Inparticular, this invention relates to a two-stage power supply suitablefor powering RF circuitry.

BACKGROUND OF THE INVENTION

RF circuitry is prone to producing communication errors from noiseand/or transients in the RF power supply. As a result, the powersupplies used in mobile wireless communications devices must be able toprovide a steady supply voltage with minimal noise.

Due to their inherent low noise characteristics, RF sections in mobilewireless communications devices are typically powered by a linearvoltage regulator. However, linear voltage regulators are typically veryinefficient. When the mobile communication device is in a sleep or lowpower consumption mode, the inefficiency of the linear voltage regulatoris of minimal concern. However, when the RF section of the mobilecommunication device is active, the inefficiency of the linear voltageregulator can dramatically shorten battery life of the device.

In contrast to linear power supplies, switch-mode power supplies (SMPSs)or push-pull voltage regulators, are typically at least 90% efficient.However, due to the noise generated from their switching transistors,SMPSs are generally not desirable for use with RF sections. Therefore,attempts have been made to devise a more efficient low-noise powersupply suitable for use with the RF section of a mobile wirelesscommunication device.

For instance, Nokkonen (U.S. Pat. No. 6,441,591) describes a powersupply that includes a battery, a SMPS and a linear voltage regulatoreach coupled to the battery, and a SMPS controller connected to theSMPS. The SMPS controller is configured with two operational modes. Inthe first mode (activated when the load current is high), the SMPS isactive, and the linear voltage regulator is powered by the SMPS. In thesecond mode (activated when the load current is low), the SMPS isinactive, and the linear voltage regulator is powered by the battery.

Since the efficiency of a linear voltage regulator diminishes with thevoltage drop across the regulator, the voltage applied to the input ofthe linear regulator during the first (high current mode) is greaterthan the voltage applied during the second (low current mode).Therefore, the efficiency of the power supply is limited by the abilityof the SMPS controller to select the appropriate operational mode basedon the prevailing load current.

SUMMARY OF THE INVENTION

According to a first aspect of the invention described herein, there isprovided a power supply that includes a switching voltage regulator, anda linear voltage regulator coupled electrically in series with theswitching voltage regulator. The switching voltage regulator includes afirst input for receiving a DC input signal, a semiconductor switchingstage coupled to the first input and configured to provide a first DCvoltage signal from the received DC input signal. The magnitude of thefirst DC voltage signal is less than the received DC input signal.

The linear voltage regulator includes a semiconductor current pass stagecoupled to the output of the semiconductor switching stage andconfigured to provide a constant second DC output voltage signal fromthe first DC voltage signal. The voltage regulators are implementedtogether within a common integrated circuit housing.

According to a second aspect of the invention described herein, there isprovided a mobile wireless communications device that includes anantenna; a data processor; an RF section coupled to the antenna and thedata processor for the communication of data between the antenna and thedata processor; a battery for providing a DC input signal; and a powersupply coupled to the battery and the RF section for supplying power tothe RF section from the DC input signal.

In the second aspect of the invention, the power supply includes aswitching voltage regulator, and a linear voltage regulator coupledelectrically in series with the switching voltage regulator. Theswitching voltage regulator includes a semiconductor switching stagecoupled to the battery and configured to provide a first DC voltagesignal from the received DC input signal. The magnitude of the first DCvoltage signal is less than the received DC input signal.

The linear voltage regulator includes a semiconductor current pass stagecoupled to the output of the semiconductor switching stage andconfigured to provide a constant second DC output voltage signal fromthe first DC voltage signal. As above, the voltage regulators areimplemented together within a common integrated circuit housing.

In one implementation, the power supply is devoid of a voltage controlloop between the linear voltage regulator and the switching voltageregulator. Also, the switching voltage regulator is configured tomaintain the magnitude of the first DC voltage signal at a voltage levelsufficient for the linear voltage regulator to maintain the magnitude ofthe second DC output voltage signal within a predetermined range.

The semiconductor current pass stage includes a controlledvoltage/current source, and a second feedback loop coupled to thecontrolled voltage/current source. Preferably, the controlledvoltage/current source comprises a transistor, and the linear voltageregulator comprises a low dropout voltage regulator. The second feedbackloop is configured to vary the magnitude of current from thevoltage/current source based on the magnitude of the second DC outputvoltage signal.

The semiconductor switching stage includes a semiconductor switch, aport coupled to the semiconductor switch for coupling to a resonantcircuit, and a first feedback loop coupled to the semiconductor switch.The first feedback loop is configured to vary the conduction interval ofthe semiconductor switch based on the magnitude of the first DC voltagesignal.

In one implementation, the power supply includes a voltage controllerthat is connected, at its output, to the input of the first feedbackloop. The first feedback loop is configured to vary the conductioninterval of the semiconductor switch based on the magnitude of the firstDC voltage signal and the voltage drop across the linear voltageregulator. The voltage controller, in co-operation with the firstfeedback loop, is configured to maintain the magnitude of the first DCvoltage signal at a voltage level that is greater than the second DCoutput voltage signal by an amount at least equal to the dropout voltageof the linear voltage regulator.

With the foregoing circuit configurations, since the voltage regulatorsare implemented together within a common integrated circuit housing,changes in the electrical characteristics of the semiconductor devicesthat implement the switching voltage regulator (due to changes inenvironmental conditions) are mirrored in the semiconductor devices thatimplement the linear voltage regulator. As a result, the power supply isable to maintain the magnitude of the output voltage of the switchingvoltage regulator above the dropout voltage of the linear voltageregulator, but without the need for complex control circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 is a front plan view of a handheld computing device having anintegrated switch mode power supply and linear regulator, according tothe invention described herein;

FIG. 2 is a schematic diagram depicting the communication pathwaysexisting between the data processing means, the LCD display, thefunction key and the data input means of the handheld computing devicedepicted in FIG. 1;

FIG. 3 is a schematic diagram depicting certain functional details ofthe handheld computing device;

FIG. 4 is a schematic diagram depicting the functional elements of oneembodiment of the integrated switch mode power supply and linearregulator; and

FIG. 5 is a schematic diagram depicting the functional elements ofanother embodiment of the integrated switch mode power supply and linearregulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a handheld computing device,denoted generally as 100, provided according to one aspect of theinvention. The handheld computing device 100 includes a display 122, afunction key 146, and data processing means 102 (not shown) disposedwithin a common housing. The display 122 comprises a backlit displayhaving a variable-intensity backlight. In one implementation, thebacklit display 122 comprises a transmissive LCD display, and thefunction key 146 operates as a power on/off switch. Alternately, inanother implementation, the backlit display 122 comprises a reflectiveor trans-reflective LCD display, and the function key 146 operates as abacklight switch.

As shown in FIG. 2, the data processing means 102 of the handheldcomputing device 100 is in communication with the display 122 and thefunction key 146. In addition to the display 122 and the function key146, the handheld computing device 100 includes user data input meansfor inputting data to the data processing means 102. As shown,preferably the user data input means includes a keyboard 132, athumbwheel 148 and an escape key 160. As will be described, the dataprocessing means 102 comprises a microprocessor 138, and a memory 124,126 (disposed within the housing). The memory 124, 126 carries computerprocessing instructions which, when accessed from the memory 124, 126and executed by the microprocessor 138, implement an operating systemand any communication-related functions, device-resident functionsand/or applications software.

Typically, the handheld computing device 100 is a two-way wirelesscommunication device having at least voice and data communicationcapabilities. Further, preferably the handheld computing device 100 hasthe capability to communicate with other computer systems on theInternet. Depending on the exact functionality provided, the wirelesshandheld computing device 100 may be referred to as a data messagingdevice, a two-way pager, a wireless e-mail device, a cellular telephonewith data messaging capabilities, a wireless Internet appliance, or adata communication device, as examples.

FIG. 3 depicts functional details of the handheld computing device 100.Where the handheld computing device 100 is enabled for two-waycommunication, the motherboard 102 will incorporate a communicationsubsystem 111, including both a radio frequency (RF) receiver 112 and aRF transmitter 114, as well as associated components such as one ormore, preferably embedded or internal, antenna elements 116 and 118,local oscillators (LOs) 113, and a processing module such as a digitalsignal processor (DSP) 120. As will be apparent to those skilled in thefield of communications, the particular design of the communicationsubsystem 111 will be dependent upon the communication network in whichthe device is intended to operate. For example, the handheld computingdevice 100 may include a communication subsystem 111 designed to operatewithin the Mobitex™ mobile communication system, the DataTAC™ mobilecommunication system, GPRS network, UMTS network, EDGE network or CDMAnetwork.

When required network registration or activation methods have beencompleted, the handheld computing device 100 may send and receivecommunication signals over the network 119. Signals received by antenna116 through communication network 119 are input to RF receiver 112,which may perform such common receiver functions as signalamplification, frequency down conversion, filtering, channel selectionand the like, and in the example system shown in FIG. 3, analog todigital (A/D) conversion. A/D conversion of a received signal allowsmore complex communication functions such as demodulation and decodingto be performed in the DSP 120. In a similar manner, signals to betransmitted are processed, including modulation and encoding forexample, by DSP 120 and input to RF transmitter 114 for digital toanalog conversion, frequency up conversion, filtering, amplification andtransmission over the communication network 119 via antenna 118. DSP 120not only processes communication signals, but also provides for receiverand transmitter control. For example, the gains applied to communicationsignals in RF receiver 112 and RF transmitter 114 may be adaptivelycontrolled through automatic gain control algorithms implemented in DSP120.

The handheld computing device 100 preferably includes a microprocessor138 which controls the overall operation of the device. Communicationfunctions, including at least data and voice communications, areperformed through communication subsystem 111. Microprocessor 138 alsointeracts with further device subsystems such as the display 122, flashmemory 124, random access memory (RAM) 126, auxiliary input/output (I/O)subsystems 128, serial port 130, keyboard 132, speaker 134, microphone136, a short-range communications subsystem 140 and any other devicesubsystems generally designated as 142.

Typically, the communication subsystem 111, flash memory 124, RAM 126,I/O subsystems 128, serial port 130, keyboard 132, speaker 134,microphone 136, microprocessor 138, and the subsystems 140, 142 areprovided on the motherboard 102, and the display 122 is provided as aself-contained unit that is physically mounted, and electricallyconnected, to the motherboard 102.

The operating system software used by the microprocessor 138 ispreferably stored in a persistent store such as flash memory 124, whichmay instead be a read-only memory (ROM) or similar storage element (notshown). Those skilled in the art will appreciate that the operatingsystem, specific device applications, or parts thereof, may betemporarily loaded into a volatile memory such as RAM 126. Receivedcommunication signals may also be stored in RAM 126.

As shown, the flash memory 124 can be segregated into different areasfor both computer programs 158 and program data storage 150, 152, 154and 156. These different storage areas indicate that each program canallocate a portion of flash memory 124 for their own data storagerequirements.

In a data communication mode, a received signal such as a text messageor web page download will be processed by the communication subsystem111 and input to the microprocessor 138, which preferably furtherprocesses the received signal for output to the display 122, oralternatively to an auxiliary I/O device 128. A user of the handheldcomputing device 100 may also compose data items such as email messagesfor example, using the keyboard 132, which is preferably a completealphanumeric keyboard or telephone-type keypad, in conjunction with thedisplay 122 and possibly an auxiliary I/O device 128. Such composeditems may then be transmitted over a communication network through thecommunication subsystem 111.

For voice communications, overall operation of the handheld computingdevice 100 is similar, except that received signals would preferably beoutput to a speaker 134 and signals for transmission would be generatedby a microphone 136.

Preferably, the RF transmitter 112 and the RF receiver 114 of thecommunication subsystem 111 are powered by a common power supply. Thepower supply is provided as an integrated circuit that is mounted on themotherboard 102. Preferred embodiments of the power supply are depictedin FIGS. 4 and 5.

The power supply 200, shown in FIG. 4, is powered by a battery 202 thatis disposed within the housing of the handheld computing device 100, andcomprises a switching voltage regulator (SMPS or switch mode powersupply) 204, and a linear voltage regulator 206. The switching voltageregulator 204 and the linear voltage regulator 206 are integratedtogether into a common integrated circuit housing.

The linear voltage regulator 206 is coupled electrically in series, atits input, with the output of the switching voltage regulator 204.However, as shown, preferably the power supply 200 is devoid of avoltage control loop between the linear voltage regulator 206 and theswitching voltage regulator 204.

The switching voltage regulator 204 comprises a first input 208 forreceiving a DC voltage from the battery 202, a resonant circuit port 210for coupling to a resonant circuit 212, and a semiconductor switchingstage 214 coupled to the first input 208 and the resonant circuit port210.

As shown, the resonant circuit 212 includes a fixed inductor 216 and acapacitor 218. The resonant circuit 212 is provided on the motherboard102, but is disposed externally to the power supply 200.

To maximize the efficiency of the power supply 200, ideally themagnitude of the voltage at the output of the switching voltageregulator 204 is less than the magnitude of the battery voltage.Accordingly, preferably the switching voltage regulator 204 isconfigured as a buck-type regulator. However, the switching voltageregulator 204 may have a different configuration. For instance, theswitching voltage regulator 204 may be configured as a boost-typeregulator where the magnitude of the voltage at the output of theswitching voltage regulator 204 is required to be greater than themagnitude of the battery voltage.

In the buck-type configuration shown, the semiconductor switching stage214 comprises a transistor switch 220 connected between the first input208 and the resonant circuit 212, a free-wheeling diode 222 connectedacross the resonant circuit 212, and a switch control circuit 224connected to the gate input of the transistor switch 220. The switchcontrol circuit 224 applies gating signals to the gate input to therebycyclically turn the transistor switch 220 on and off.

Preferably, the switching voltage regulator 204 also includes a firstfeedback loop for controlling the DC output voltage of the switchingvoltage regulator 204. In the example shown, the switching voltageregulator 204 includes a feedback control input 227 that is connected tothe output of the switching voltage regulator 204, and the firstfeedback loop is implemented using a pulse-width controller 226 that isdisposed between the switch control circuit 224 and the feedback controlinput 227. The pulse-width controller 226 adjusts the conductioninterval of the transistor switch 220 based on the magnitude of thevoltage at the output of the switching voltage regulator 204 (asmeasured at the feedback control input 227).

With the foregoing configuration, the switching voltage regulator 204maintains the magnitude of the DC voltage signal at the output of thesemiconductor switching stage 214 substantially constant.

The linear voltage regulator 206 is configured to provide a constant DCoutput voltage signal from the first DC voltage signal that is outputfrom the switching voltage regulator 204. As shown, the linear voltageregulator 206 comprises a semiconductor current pass stage 228 that iscoupled to the output of the semiconductor switching stage 214.

To maximize the efficiency of the power supply 200, preferably thelinear voltage regulator 206 is configured as a low-dropout (LDO)voltage regulator. However, the linear voltage regulator 206 may have adifferent configuration.

In the low-dropout configuration shown, the semiconductor current passstage 228 comprises a transistor 230, and a feedback loop forcontrolling the DC output voltage of the linear voltage regulator 206.In the example shown, the second feedback loop is implemented using anoperational amplifier 232 that is disposed between the base of thetransistor 230 and the output of the linear voltage regulator 206. Thetransistor 230 acts as a voltage/current source, and the operationalamplifier 232 varies the magnitude of current through thevoltage/current source based on the magnitude of the voltage at theoutput of the linear voltage regulator 206.

The linear voltage regulator 206 is configured to maintain the magnitudeof the voltage at the output of the linear voltage regulator 206 withina predetermined range. However, to ensure that the linear voltageregulator 206 is able to maintain the output voltage of the within thepredetermined range, the switching voltage regulator 204 is configuredto maintain the voltage at the output of the semiconductor switchingstage 214 above the output voltage of the power supply 200 by an amountat least equal to the dropout voltage of the linear regulator 206.

Turning now to FIG. 5, the power supply 300 shown therein is powered bythe battery 202 that is disposed within the housing of the handheldcomputing device 100, and comprises the switching voltage regulator 204,the linear voltage regulator 206, and a voltage controller 306. Theswitching voltage regulator 204, the linear voltage regulator 206, andthe voltage controller 306 are integrated together into a commonintegrated circuit housing.

The linear voltage regulator 206 is coupled electrically in series, atits input, with the output of the switching voltage regulator 204. Thevoltage controller 206 is connected between the switching voltageregulator 204 and the linear voltage regulator 206.

As discussed above, the linear voltage regulator 206 is configured toprovide a constant DC output voltage signal from the first DC voltagesignal that is output from the switching voltage regulator 204. Toensure that the linear voltage regulator 206 is able to do so, thevoltage controller 306 is connected at its output to the feedbackcontrol input 227 of the switching voltage regulator 204, to therebymaintain the voltage at the output of the switching voltage regulator204 above the output voltage of the power supply 300 by an amount thatis at least equal to the dropout voltage of the linear regulator 206.However, to enhance the efficiency of the power supply 300, preferablythe voltage controller 306 maintains the output voltage of the switchingvoltage regulator 204 at a magnitude that is equal to the sum of theoutput voltage of the linear regulator 206 and the voltage drop acrossthe linear regulator 206.

Accordingly, the voltage controller 306 is configured to continuouslymeasure the voltage drop across the linear voltage regulator 206, and toadjust the output voltage of the switching voltage regulator 204 basedon the output voltage of the switching voltage regulator 204 and themeasured voltage drop of the linear voltage regulator 206.

As shown, the voltage controller 306 comprises a voltage comparator 330,and a voltage adder 332. The voltage comparator 330 comprises adifferential amplifier U1, a first voltage divider 334 (comprisingresistors R1, R2) connected to the inverting input of the differentialamplifier U1, and a second voltage divider 336 (comprising resistors R1,R2) connected to the non-inverting of the differential amplifier U1. Thevoltage adder 332 comprises a differential amplifier U2, a third voltagedivider 338 (comprising resistors R3, R4) connected to the invertinginput of the differential amplifier U2, and a fourth voltage divider 340(comprising resistors R3, R4) connected to the non-inverting of thedifferential amplifier U2.

As will be apparent from the foregoing resistor nomenclature, theresistance of the resistor R1 of the first voltage divider 334 is equalto the resistance of the resistor R1 of the second voltage divider 336.Similarly, the resistance of the resistor R2 of the first voltagedivider 334 is equal to the resistance of the resistor R2 of the secondvoltage divider 336. Similar comments apply to the resistors R3 of thethird and fourth voltage dividers 338, 340, and the resistors R4 of thethird and fourth voltage dividers 338, 340.

The voltage comparator 330 is connected at its inverting input to thevoltage output of the linear voltage regulator 206 (via the resistor R1of the first voltage divider 334), and is connected at its non-invertinginput to the voltage output of the switching voltage regulator 204 (viathe resistor R1 of the second voltage divider 336). Therefore, thevoltage output by the voltage comparator 330 is proportional to thevoltage drop across the linear voltage regulator 206.

The voltage adder 332 is connected at its inverting input to the voltageoutput of the voltage comparator 330 (via the resistor R3 of the thirdvoltage divider 340), and is connected at its non-inverting input to thevoltage output of the switching voltage regulator 204 (via the resistorR3 of the fourth voltage divider 340). The voltage adder 332 isconnected at its output to the feedback control input 328 of theswitching voltage regulator 204. Therefore, the voltage at the feedbackcontrol input 227 is proportional to the difference between the voltageoutput by the switching voltage regulator 204 and the voltage dropacross the linear voltage regulator 206.

In particular:V ₃₃₀=(R2/R1)×V _(DROP) _(—) _(LDO);V ₃₃₂=(R4/R3)×(V _(SMPS) −V ₃₃₀);where:

V₃₃₀ is the voltage output by the voltage comparator 330;

V₃₃₂ is the voltage output by the voltage adder 332;

V_(DROP) _(—) _(LDO) is the voltage drop across the linear voltageregulator 206; and

V_(SMPS) is voltage output by the switching voltage regulator 204

Preferably, (R2/R1)=(R4/R3)=1, so that V₃₃₂=(V_(SMPS)−V_(DROP) _(—)_(LDO))

In configuration shown in FIG. 5, the switching voltage regulator 204still maintains the magnitude of the DC voltage signal at the output ofthe semiconductor switching stage 214 substantially constant. However,since the feedback control input 227 is connected to the output of thevoltage controller 306 (as opposed to the output of the switchingvoltage regulator 204), the first feedback loop of the switching voltageregulator 204 increases the output voltage of the switching voltageregulator 204 by the voltage drop across the linear regulator 206.

In other words, the switching voltage regulator 204 maintains its outputvoltage at a magnitude that is equal to the sum of the output voltage ofthe power supply 300 and the voltage drop across the linear regulator206. In this manner, the voltage controller 306 is able to maintain thevoltage at the output of the switching voltage regulator 204 above theoutput voltage of the power supply 300 by an amount that is at leastequal to the dropout voltage of the linear regulator 206.

With each of the foregoing circuit configurations, since the voltageregulators 204, 206 (and the voltage controller 306, if used) areimplemented together within a common integrated circuit housing, thesemiconductor devices contained therein are all exposed to the sameenvironmental conditions, such as ambient temperature and humidity. As aresult, changes in the electrical characteristics of the semiconductordevices that implement the switching voltage regulator 204 (due tochanges in environmental conditions) are mirrored in the semiconductordevices that implement the linear voltage regulator 206 (and the voltagecontroller 306).

The resulting matching of electrical characteristics allows theswitching voltage regulator 204 to maintain the magnitude of the outputvoltage of the switching voltage regulator 204 above the dropout voltageof the linear voltage regulator 206. In the embodiment shown in FIG. 4,this result is achieved without a voltage control loop between thelinear voltage regulator 206 and the switching voltage regulator 204. Inthe embodiment shown in FIG. 5, this result is achieved using a simpleadder circuit between the linear voltage regulator 206 and the switchingvoltage regulator 204. In each embodiment, the power supply 200 is ableto maintain the output voltage of the linear voltage regulator 206substantially constant, without using complex control circuitry.

The scope of the monopoly desired for the invention is defined by theclaims appended hereto, with the foregoing description being merelyillustrative of the preferred embodiment of the invention. Persons ofordinary skill may envisage modifications to the described embodimentwhich, although not explicitly suggested herein, do not depart from thescope of the invention, as defined by the appended claims.

1. A power supply comprising: a switching voltage regulator, theswitching voltage regulator comprising a first input for receiving a DCinput signal, a semiconductor switching stage coupled to the first inputand being configured to provide a first DC voltage signal from thereceived DC input signal, a magnitude of the first DC voltage signalbeing less than the received DC input signal; and a linear voltageregulator coupled electrically in series with the switching voltageregulator, the linear voltage regulator comprising a semiconductorcurrent pass stage coupled to an output of the semiconductor switchingstage and being configured to provide a constant second DC outputvoltage signal from the first DC voltage signal, wherein the powersupply is devoid of a voltage control loop between the linear voltageregulator and the switching voltage regulator.
 2. The power supplyaccording to claim 1, wherein the voltage regulators are implementedtogether within a common integrated circuit housing.
 3. The power supplyaccording to claim 1, wherein the switching voltage regulator isconfigured to maintain a magnitude of the first DC voltage signal at avoltage level sufficient for the linear voltage regulator to maintain amagnitude of the second DC output voltage signal within a predeterminedrange.
 4. The power supply according to claim 3, wherein thesemiconductor current pass stage comprises a controlled current source,and a second feedback loop coupled to the controlled current source, thesecond feedback loop being configured to vary a magnitude of currentfrom the current source based on a magnitude of the second DC outputvoltage signal.
 5. The power supply according to claim 4, wherein thecontrolled current source comprises a transistor, and the linear voltageregulator comprises a low dropout voltage regulator.
 6. A mobilewireless communications device comprising: an antenna; a data processor;an RF section coupled to the antenna and the data processor for thecommunication of data between the antenna and the data processor; abattery for providing a DC input signal; and a power supply coupled tothe battery and the RF section for supplying power to the RF sectionfrom the DC input signal, the power supply including: a switchingvoltage regulator, the switching voltage regulator comprising asemiconductor switching stage coupled to the battery and beingconfigured to provide a first DC voltage signal from the received DCinput signal, a magnitude of the first DC voltage signal being less thanthe received DC input signal; and a linear voltage regulator coupledelectrically in series with the switching voltage regulator, the linearvoltage regulator comprising a semiconductor current pass stage coupledto an output of the semiconductor switching stage and being configuredto provide a constant second DC output voltage signal from the first DCvoltage signal, wherein the power supply is devoid of a voltage controlloop between the linear voltage regulator and the switching voltageregulator.
 7. The mobile wireless communications device according toclaim 6, wherein the voltage regulators are implemented together withina common integrated circuit housing.
 8. The mobile wirelesscommunications device according to claim 7, wherein the switchingvoltage regulator is configured to maintain a magnitude of the first DCvoltage signal at a voltage level sufficient for the linear voltageregulator to maintain a magnitude of the second DC output voltage signalwithin a predetermined range.
 9. The mobile wireless communicationsdevice according to claim 8, wherein the semiconductor current passstage comprises a controlled current source, and a second feedback loopcoupled to the controlled current source, the second feedback loop beingconfigured to vary a magnitude of current from the current source basedon a magnitude of the second DC output voltage signal.
 10. The mobilewireless communications device according to claim 9, wherein thecontrolled current source comprises a transistor, and the linear voltageregulator comprises a low dropout voltage regulator.
 11. A power supplycomprising: a switching voltage regulator, the switching voltageregulator comprising a first input for receiving a DC input signal, asemiconductor switching stage coupled to the first input and beingconfigured to provide a first DC voltage signal from the received DCinput signal, a magnitude of the first DC voltage signal being less thanthe received DC input signal; a linear voltage regulator coupledelectrically in series with the switching voltage regulator, the linearvoltage regulator comprising a semiconductor current pass stage coupledto an output of the semiconductor switching stage and being configuredto provide a constant second DC output voltage signal from the first DCvoltage signal; and a voltage controller disposed between the linearvoltage regulator and the switching voltage regulator and configured tomaintain a magnitude of the first DC voltage signal at a voltage levelsufficient for the linear voltage regulator to maintain a magnitude ofthe second DC output voltage signal within a predetermined range. 12.The power supply according to claim 11, wherein the voltage regulatorsand the voltage controller are implemented within a common integratedcircuit housing.
 13. The power supply according to claim 11, wherein thevoltage controller is configured to maintain the magnitude of the firstDC voltage signal at a voltage that is greater than the magnitude of thesecond DC output voltage signal by an amount at least equal to a dropoutvoltage of the linear voltage regulator.
 14. The power supply accordingto claim 13, wherein the maintained voltage is equal to the magnitude ofthe second DC output voltage signal and a voltage drop across the linearvoltage regulator.
 15. The power supply according to claim 11, whereinthe semiconductor switching stage includes a semiconductor switch, aport coupled to the semiconductor switch for coupling to a resonantcircuit, and a first feedback loop coupled to the semiconductor switch,the first feedback loop being configured to vary a conduction intervalof the semiconductor switch based on the magnitude of the first DCvoltage signal.
 16. A mobile wireless communications device comprising:an antenna; a data processor; an RF section coupled to the antenna andthe data processor for the communication of data between the antenna andthe data processor; a battery for providing a DC input signal; and apower supply coupled to the battery and the RF section for supplyingpower to the RF section from the DC input signal, the power supplyincluding: a switching voltage regulator, the switching voltageregulator comprising a semiconductor switching stage coupled to thebattery and being configured to provide a first DC voltage signal fromthe received DC input signal, a magnitude of the first DC voltage signalbeing less than the received DC input signal; a linear voltage regulatorcoupled electrically in series with the switching voltage regulator, thelinear voltage regulator comprising a semiconductor current pass stagecoupled to an output of the semiconductor switching stage and beingconfigured to provide a constant second DC output voltage signal fromthe first DC voltage signal; and a voltage controller disposed betweenthe linear voltage regulator and the switching voltage regulator andconfigured to maintain a magnitude of the first DC voltage signal at avoltage level sufficient for the linear voltage regulator to maintain amagnitude of the second DC output voltage signal within a predeterminedrange.
 17. The mobile wireless communications device according to claim16, wherein the voltage regulators and the voltage controller areimplemented within a common integrated circuit housing.
 18. The mobilewireless communications device according to claim 16, wherein thevoltage controller is configured to maintain the magnitude of the firstDC voltage signal at a voltage that is greater than the magnitude of thesecond DC output voltage signal by an amount at least equal to a dropoutvoltage of the linear voltage regulator.
 19. The mobile wirelesscommunications device according to claim 18, wherein the maintainedvoltage is equal to the magnitude of the second DC output voltage signaland a voltage drop across the linear voltage regulator.
 20. The mobilewireless communications device according to claim 16, wherein thesemiconductor switching stage includes a semiconductor switch, a portcoupled to the semiconductor switch for coupling to a resonant circuit,and a first feedback loop coupled to the semiconductor switch, the firstfeedback loop being configured to vary a conduction interval of thesemiconductor switch based on the magnitude of the first DC voltagesignal.